A common problem in mechanisms is to arrest or resist rectilinear motion of mechanical parts, and a common solution is a piston-cylinder assembly having a restricted passage from one side of the piston to the other. It is frequently desirable to provide some means of varying the restriction with the position of the piston along its stroke; by this means the resistance to motion can be tailored to achieve desired values as functions of velocity and position of the piston with respect to the cylinder. Many arrangements for achieving an orifice variable with piston position have been developed, the most common perhaps, involving a circular orifice in the piston through which passes a tapered rod attached to the cylinder, often used in aircraft landing gear shock struts. Other devices may incorporate grooves of varying depth in the cylinder wall (U.S. Pat. No. 695,775), tapered cylinders in which a fixed diameter piston operates (U.S. Pat. No. 3,062,331), or more or less complex valves in the passage.
The objectives sought and achieved by the present device include simplicity of manufacture, ease of altering the resistance characteristics, ready adaptability to incorporation into relatively complex actuating mechanisms, low cost, and trouble-free operation.